The high demand in petrochemistry for lower hydrocarbons such as saturated and unsaturated aliphatic, cycloaliphatic or aromatic hydrocarbons is satisfied by conversion processes such as catalytic cracking, hydrocracking or thermal cracking. The feedstocks used are crude oils or relatively high-boiling crude oil distillate fractions.
In catalytic cracking, preference is given to working with fluidized beds consisting of zeolites (FCC processes). The zeolites are used in the H form, which can be produced by heating corresponding zeolites comprising ammonium ions and preferably cations of rare earth metals to about 400° C. (Hans-Jürgen Arpe, Industrielle organische Chemie [Industrial Organic Chemistry], 6th edition, 2007, Wiley-VCH publishers, pages 64 to 65).
For instance, U.S. Pat. No. 3,966,882 describes the exchange of Na for NH4 ions Ammonium carbonate is not mentioned.
US Re28,629 and U.S. Pat. No. 4,346,067 disclose using ammonium chloride, ammonium nitrate or ammonium sulfate for ion exchange. In examples 1 to 3 and 8, for example, sodium ions present in Y zeolites are exchanged for ammonium ions using aqueous ammonium sulfate solutions. Example 6 describes the exchange of sodium ions in Y zeolites for rare earth metal cations. In example 7, the exchange of sodium ions in an X zeolite for rare earth cations and calcination are followed by an exchange of sodium ions for ammonium ions.
U.S. Pat. No. 4,346,067 also mentions that, apart from the ammonium compounds, urea may also be present. Tables I and II in example 1C show that, with aqueous urea in the absence of ammonium compounds, 9.18−8.17%=0.61% of the original amount of Na is still exchanged. This can be explained by hydrolysis of the urea to ammonium carbonate and subsequent ion exchange.
CN 101623650 mentions that ammonium carbonate is used for ion exchange.
The exchange between zeolite comprising sodium ions, for example a sodium Y zeolite, and an ammonium salt, for example ammonium nitrate, constitutes an equilibrium reaction. In order to exchange the sodium ions or rare earth metal cations very substantially for ammonium ions, the zeolite has to be treated several times in succession, preferably at temperatures of 70° C. to 100° C., in some cases to 200° C., with an excess of aqueous ammonium nitrate or rare earth metal salts relative to the sodium ions. After the ion exchange step, the salt solution is generally separated from the zeolite. The solid zeolite can subsequently be washed with water in order to remove salts. After each ion exchange step, it is calcined at 200° C. to 600° C. In the course of this, ammonia release from the ammonium ions forms the desired H form of the zeolite (Ullmann's Encyclopedia of Industrial Chemistry, 6th edition, volume 39, 2003, Wiley-VCH publishers, pages 638 to 640).
As a result of the ion exchange and the calcination, the Y zeolite in the H form, preferably comprising cations of the rare earth metals, and an aqueous salt solution comprising a mixture of sodium nitrate and unconverted ammonium nitrate are obtained. Since the replacement of the sodium ions by the ammonium ions and the cations of the rare earth metals is incomplete, ammonium compounds and salts of the rare earth metals are present alongside sodium compounds in the mother liquor.
The thermal release of ammonia and carbon dioxide from an aqueous ammonium carbonate solution is described in WO 2009/036145. For instance, FIG. 1 shows that ammonia and water are first released from ammonium hydrogencarbonate/sodium carbonate mixtures and the remaining sodium hydrogencarbonate is converted to sodium carbonate with release of carbon dioxide.
Hollemann-Wiberg, Lehrbuch der Anorganischen Chemie [Inorganic Chemistry], 102 nd edition (2007), Walter de Gruyter publishers, page 671, “Ammoniumcarbonat” section, it is known that ammonium carbonate can be produced by introducing carbon dioxide into aqueous ammonia.
One disadvantage in the prior art processes is that large amounts of aqueous sodium nitrate and ammonium nitrate solution, sodium sulfate and ammonium sulfate solution or sodium chloride and ammonium chloride solution are formed, which are obtained, for example, in the case of use of ammonium nitrate, ammonium sulfate or ammonium chloride in the ion exchange of zeolites comprising sodium ions.
A further disadvantage is that not inconsiderable amounts of salts of the rare earth metals are leached out of the zeolites.
The salt solutions can in principle be used for production of fertilizers. However, this means only a low level of added value. Moreover, the economic viability of utilization as a fertilizer depends on the site.
The ammonia bound in the ammonium salts can be released by addition of at least equimolar amounts of sodium hydroxide solution, removed by stripping or distillation and reused for the preparation of the ammonium salts. However, this addition of value is reduced by the consumption of sodium hydroxide solution. There remains a large amount of the respective aqueous sodium salt solution. If there is no means of further use, it has to be disposed of. The known processes require high circulation rates with a considerable energy requirement, which constitutes an economic disadvantage.
The recovery of rare earth metals constitutes an additional, complex process step.